1. Technical Field
Some aspects according to the present invention relate to an optical device, an optical scanner, and an image forming apparatus produced, for example, by using a MEMS (Micro Electro Mechanical System) technology and having a movable plate moving around an elastic support portion in a reciprocating motion.
2. Related Art
An optical device of this type has been known as an optical scanner including a mirror/magnet assembly swingably supported by a shape-memory alloy wire, and the optical scanner is formed by separately preparing a mirror and a magnet and bonding and securing them with the shape-memory alloy wire interposed therebetween. The durability of the optical scanner can be enhanced because the above configuration improves the adhesion force between the mirror/magnet assembly and the shape-memory alloy wire (see JP-A-9-304721, for example).
The optical device of the related art, however, is problematic in that when the mirror/magnet assembly is in a swing motion, a force produced by torsional deformation of the axis member is transferred to the mirror/magnet assembly and huge local bending (distortion) is produced in the portion of the mirror/magnet assembly that is connected to the shape-memory alloy wire. To prevent the bending (distortion) of the mirror/magnet assembly, for example, increasing the thickness of the mirror/magnet assembly causes the following problem: When the oscillation system formed of the mirror/magnet assembly and the shape-memory alloy wire is oscillated (in a swing motion) at a fixed number of oscillation (frequency), the necessary length of the wire needs to be longer than that in an oscillation system with the thickness of the mirror/magnet assembly unchanged. As a result, the optical device becomes disadvantageously larger in size.